The present application claims priority under 35 USC 119 from Great Britain application No. GB9721818.4, entitled THERMALLY ISOLATED SILICON LAYERxe2x80x9d filed Oct. 16, 1997. The disclosures of the referenced application is hereby incorporated herein by reference.
This invention relates to an integrated optical circuit formed in a silicon layer and supported on a substrate with at least a portion of the silicon layer being substantially thermally isolated from the substrate.
Temperature control of integrated optical devices, particularly silicon-on-insulator (SOI) waveguides, is desirable in order to adjust the refractive index of the device (the refractive index of silicon increases by a factor of 2xc3x9710xe2x88x924 per degree C, which is a relatively large change compared to other optical materials).
Prior art such as EP-A-0255270 proposes the use of a recess in a silicon substrate in order to thermally isolate a silica waveguide extending there over to avoid thermal stresses in the waveguide due to the different thermal expansion coefficients of silicon and silica. This prior art also discloses forming the waveguide as a cantilever structure to provide an on-off switch activated by displacement of the cantilevered waveguide.
It is therefore an object of the present invention to provide an integrated optical circuit formed in a silicon layer and supported on a substrate.
It is a further object of the present invention to substantially thermally isolate a portion of the silicon layer from the substrate by extending the silicon layer over a recess in the substrate.
It is a further object of the present invention to provide a temperature control means to control the temperature of the portion of the silicon layer or of a device provided thereon.
Preferred and optional features of the invention will be apparent from the subsidiary claims of the specification.
The invention will now be further described, merely by way of example, with reference to the accompanying drawings, in which: